Historically, in order to prevent scale deposition, corrosion of metal surfaces and similar fouling of water treatment systems, as well to maintain proper pH levels, anti-foulants, anti-scaling agents, corrosion inhibitors, buffering and pH agents, microcides and the like have been added directly to water treatment systems on an as needed basis. Typically, a system is monitored, such as by recovering and analyzing a sample, in order to determine the current level of particular chemical treatment agents. When the concentration of a particular agent falls below a desired level, additional agent is added to the system.
Numerous techniques have been used in the past to treat coolant systems. For example, antifreeze compositions have been formulated to meet the demands of automobile engine coolant systems. However, conventional antifreeze compositions are insufficient to meet the unique demands imposed on diesel engine coolant systems. As a result, supplemental coolant additives (SCA) are added to diesel engine coolant systems to make up for the deficiencies of antifreeze formulations. Typically, supplemental coolant additives are added to the diesel engine coolant system at each oil change in order to replace additives which have been diluted or depleted from the system.
Other methods of introducing supplemental coolant additives to the diesel engine coolant system have been developed. For instance, it is known to add a solid SCA material directly to the diesel engine coolant system which dissolves in the coolant system. In this manner, it is expected that a minimum level of supplemental coolant additives will remain in the diesel engine coolant system for a predetermined time. However, there are significant drawbacks to using a solid SCA material including the danger of overdosing the system with particular additives which can result in erosion and corrosion problems. Further, this technique does not maintain a consistent concentration level of supplemental coolant additives within the system.
Another attempt to deliver supplemental coolant additives to a diesel engine system is the use of coolant filters which contain supplemental coolant additives. These devices operate as bypass filters with coolant flowing through the filter and extracting the supplemental coolant additive. Although the use of coolant filters is all improvement over the use of a supplemental coolant additive block, the danger of overdosing the system still exists and a controlled, minimal concentration level of supplemental coolant additives cannot be maintained within the system.
Minimal attempts have been made in the prior art to address particular water treatment systems by using controlled release capsules. U.S. Pat. No. 4,561,981 issued on Dec. 31, 1985 to William G. Characklis discloses a method for controlling, preventing or removing fouling deposits, particularly in pipelines, storage tanks and the like by microencapsulating fouling control chemicals in a slow release capsule. The encapsulating material is described as being any material compatible with the fouling control chemical which is capable of sticking to the fouling deposit site. A likely result of introducing the encapsulating material directly into the water treatment system is that the encapsulating material will deteriorate and create additional corrosion problems. Further, due to the sticky nature of Characklis' controlled release capsule it is unsuitable for use in engine coolant systems.
Controlled release formulations are well known in the art for non-water treatment applications. U.S. Pat. No. 5,186,732 issued Feb. 16, 1993 to Harold E. Thompson et al. discloses an encapsulated slow release fertilizer which provides prolonged leaching of a water soluble agent by utilizing an encapsulated coating comprises a water-borne, polyvinylidene chloride based latex composition. U.S. Pat. No. 5,120,349 issued Jun. 9, 1992 to Ray F. Stewart et al. provides a microcapsule having a heat sensitive crystallizable polymeric coating comprising a polymer backbone and 1 to 10% of a polar functional group. However, neither of the patents teaches encapsulating conventional water treatment chemicals such as anti-scaling agents, corrosion inhibitors, anti-foulants and the like for use in the treatment of water systems.
Despite the efforts of the prior art, a need still exists for a controlled release water treatment chemical which will provide a consistent level of treatment chemicals to the system over an extended period of time. In particular, the prior art has failed to develop a controlled release supplemental coolant additive which slowly releases supplement coolant additive (SCA) components to a diesel engine coolant system. Such a controlled release supplement coolant additive should deliver a consistent concentration of SCA components to a diesel engine coolant system, should not overdose the system with SCA components and should be capable of maintaining an effective concentration level of SCA compositions over a desired period of time.